In EP-0 244 517 B1, a knife is described in which, within a hollow handle, a blade holder is longitudinally shiftable and is retracted by an elongated tension coil spring anchored to the holder, the pawl of this device, which engages a tooth on the holder and can serve as an inertial mass which is dislodged from the tooth upon a centrifugal action of the blade.
That device provides the pawl with spring loading against the holder so that, when the blade holder is shifted within the hollow handle toward the opening of the latter so that the blade will protrude through this opening, the holder will be locked or retained in the operative or extended position of the blade. A gravitational or centrifugal action can be used to project the blade from the holder.
In practice it has been found that the pawl required a rather excessive range of motion of the knife to effect its release. Stated otherwise, the sensitivity of the pawl to slipping of the knife or some manipulation which requires the safety action of withdrawal of the blade was limited.
In general, therefore, an excessive displacement of the knife to effect retraction of the blade means that the knife is not as safe as is desirable.